Main controlling factors for carbonate rock distribution on the southern slope of Chezhen Sag, Bohai Bay Basin

The distribution of carbonate rocks on the southern slope of Chezhen Sag in Bohai Bay Basin was stu-died using well logging, drilling and testing data. Carbonate rocks mainly distribute in the upper section of the fourth member of Shahejie Formation, including micrite limestones, biolithite limestones, argillaceous limestones and dolomites. The study area had a landscape pattern of "two subsags and one uplift in the middle" during the deposition of the upper section of the fourth member of Shahejie Formation, which determined the distribution and thickness of carbonate rocks. The study area belonged to shore-shallow lake environment. Carbonate rocks developed at about 11-50 m depth, and most developed at 34 m. From the early to the late period of the deposition of the upper section of the fourth member of Shahejie Formation, paleoclimate changed from dry to humid, and the distribution range of gypsum rocks gradually narrowed while that of carbonate rocks expanded. With the combined function of ancient landscape,water depth and paleoclimate, clastic rocks, argillaceous limestones, biolimestones, micrites, dolomites, gypsum-salt rocks, argillaceous limestones and calcareous rocks were depo-sited from basin edge to center. A sedimentary model for the deposition of carbonate rocks was established.